This invention provides an earth anchor that has been developed primarily in conjunction with the stabilizing and re-positioning of basement walls that are in danger of being displaced by outside earth pressure. In freezing conditions, soil moisture solidifies, and expands with tremendous force. In warmer weather, the thawing ground relaxes the pressure, and sometimes withdraws as it contracts. The resulting gap can easily become at least partially filled, causing a renewed pressure layer against the already displaced basement wall when the ground freezes again. Resulting cracks in the wall invite the invasion of ground water into the basement, which is another factor that has focused attention on the problem of wall instability.
Attempts have been made to stabilize basement walls against further displacement, and even return them to a vertical plane. One expedient (shown in the Johnson, et al, U.S. Pat. No. 4,189,891) involves digging an excavation at some distance out from the wall, and drilling a hole through the wall opposite the excavation. A rod is then driven through the earth from this hole, which is secured to some object deposited in the excavation. The excavation is then filled in, and the rod can function as a long bolt terminating inside the wall at a nut and a bearing plate. A much simpler system is described in the Harmon U.S. Pat. No. 4,970,835, issued on Nov. 20, 1990. This system requires no excavation, and replaces the buried terminal with an expandable earth anchor inserted in the hole in the basement wall, and driven out into the earth with the bolt rod. Pulling on the rod by tightening the nut against a bearing plate inside the basement wall opens the anchor device ultimately to a fully expanded position. In both of these systems, the bearing nuts can be periodically tightened to re-position the wall. An anchor device of this type can be expected to be inserted in a variety of different types of soil, ranging from solid clay, to pure sand. As the anchor is forced through the soil on installation, it will tend to produce a well-defined hole in a solid clay-type soil. With sand, however, the hole is less well-defined. It tends to fall back around the bolt rod as the anchor device is forced into position. The return pull on the rod by tightening the nut inside the basement wall causes the anchor device to readily dig into the loose soil, but can conceivably pull it right back through the hole that it has formed in a more solid soil. A need has been found for assuming an initial expansion of the anchor device sufficient to dig it into the walls defining the hole, regardless of whether or not the earth has tended to fill in behind the anchor as it was driven into position. The structure of these anchors centers in a threaded central portion to which arms are pivotally connected, and which trail from the pivot connection back along the bolt rod as the anchor is driven. On opposite movement of the bolt rod, however, they are opened by earth pressure into a position approaching 90.degree. from the axis of the rod, where a stop limits further rotation. The problem here is to provide a system for initiating the expansion of the anchor that can be controlled by the bolt rod from the inside of the basement wall.
In the looser types of soil, it also may be necessary to increase the anchoring effect by the use of multiple anchor devices on the same bolt rod. This simply means increasing the number of the pivoted arms that become subject to earth pressure. These arms are analogous to the "flukes" common in marine anchors.